Abstract
The excavation of the flood plain sometimes makes three-stage flow, which is composed of a main channel, a flood plain and a mid-level concavity land. In order to maintain this type ofconcavity in the flood plain, it is necessary to understand the flow structures. In this study, three-dimensional flow structures in concavity zones in compound open channels were investigated experimentally. The time-averaged flow structures in concavity zones were revealed by using PIV method. The shape of concavity and the relative level of the concavity bed was changed and investigated their effects on the flow structures in the concavity zones. Furthermore, sediment deposition tests was conducted in the same laboratory flume and the relation offlow structures to sediment transport process was investigated. In rectangular concavity case, the longitudinal scale of the transverse vortex becomes larger relative to the vertical vortex with an increase of the depth of the concavity. In trapezoidal concavity, a skew step produces inclined transverse vortex and generates different flow patterns from the normal step case. The bed level difference provides dissimilar flow structures and sediment deposition rate in the concavity zones.
